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Flashcards · 9618 · AS Topic 3

Hardware (AS Level) flashcards

14 cards on AS Topic 3, subtopics 3.1 to 3.2. Pick a subtopic or study them all.

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3.1 Computers and their components

What is the difference between RAM and ROM?
RAM: volatile, read and write, holds the programs and data currently in use. ROM: non-volatile, read only (in normal use), holds fixed start-up instructions such as the bootstrap.
What is the difference between SRAM and DRAM?
DRAM stores each bit as a charge on a capacitor and must be refreshed constantly; it is cheaper and denser, so used for main memory. SRAM uses flip-flops, needs no refresh and is faster, so used for cache.
What are PROM and EPROM?
PROM: programmable once after manufacture, then cannot be changed. EPROM: can be erased (using ultraviolet light) and reprogrammed.
What is the difference between magnetic, optical and solid-state storage?
Magnetic (hard disk): data stored as magnetised regions on spinning platters. Optical (CD, DVD): pits and lands read by a laser. Solid-state (flash): charge stored in transistors, no moving parts, so faster access.
What is an embedded system?
A computer system built into a larger device to perform one dedicated function, e.g. in a washing machine or a car engine management unit.
What is the role of sensors and actuators in a control system?
Sensors measure physical quantities (temperature, light, pressure) and send data to the processor. Actuators carry out physical actions (motors, valves, heaters) in response to the processor’s output. Feedback lets the system adjust its output.
How does EEPROM differ from EPROM?
EPROM is erased with ultraviolet light, usually after removing the chip from the device. EEPROM is erased and rewritten electrically while it stays in the circuit, so firmware can be updated in place.
What is a buffer used for?
A temporary area of memory that holds data being transferred between devices working at different speeds, e.g. the processor fills a printer buffer and continues other work while the printer empties it.
Monitoring system vs control system
Monitoring: sensors take readings, which are compared with stored values and displayed, recorded or used to warn; conditions are not changed. Control: actuators are also used to change the conditions.
Why is feedback important in a control system?
After an actuator acts, new sensor readings are taken and compared again, so the output affects the next input and conditions are kept near the target continuously.

3.2 Logic Gates and Logic Circuits

When is the output of an AND gate and of an OR gate 1?
AND: only when both inputs are 1. OR: when at least one input is 1.
When is the output of a NAND gate and of a NOR gate 1?
NAND (NOT AND): 1 unless both inputs are 1. NOR (NOT OR): 1 only when both inputs are 0.
When is the output of an XOR gate 1?
When the inputs are different (one is 1 and the other 0).
How many rows does a truth table need for a circuit with n inputs?
2ⁿ rows. Three inputs need 8 rows, listed in binary order 000 to 111.

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